1. Field of the Invention
The present invention relates to a printer with a sensor for detecting a printing medium to be set in the printer, and more particularly to a cleaning mechanism for cleaning the sensor and a control method for the cleaning mechanism.
2. Description of the Related Art
For printing on forms, slips or the like, the printer has been widely used as the output terminal of POS systems, computer systems, personal computers and others. Some printers print each on a printing sheet, e.g., a roll paper, which is preset therein, and some printer include each a mechanism for printing on cut sheets, e.g., validation sheets, which are set one by one therein by the user.
The printer usually uses a photo sensor to check as to if a printing paper is set properly or at a correct position before the printing by the printer. The photo sensor includes the combination of a light emitting element, e.g., LED, and a light sensing element, e.g., a photo transistor. Those elements are arrayed while being spaced from each other. When a printing sheet is set in the printer, it interrupts a light beam emitted from the LED. By the interruption of the light beam, the photo sensor detects the setting of the printing paper in the printer.
The conventional printer suffers from the following problem. Various dusts such as paper dust or the like are accumulated on and around the sensor, and the accumulated dust interrupts the optical path of the light beam. As the accumulation of the dust progresses, the output signal of the photo sensor decreases. When the output level of the photo sensor goes below a predetermined signal level, the printer mistakenly recognizes this state as the setting of the printing paper, and erroneously operates.
Further, strict requirements are imposed on recent printers; high reliability, and some measures being taken for environmental issues such as long life, use of regenerated papers being acceptable and so on. Dusts generated therein are easily increased in those printers which are designed to satisfy such requirements.